It has been known recently to widely use melting equipment operating on gaseous fuel, more particularly, natural gas. When melting of cast iron is done by the use of natural gas, the metal is not saturated with noxious sulphur admixtures and the strength of iron castings is increased since there is no detrimental slag inclusions inherent in melting on coke.
Furthermore, the simplicity of natural gas transport and the high combustion heat of natural gas are of substantial importance. The use of natural gas as a fuel reduces air pollution.
Owing to the aforementioned advantages of natural gas and the growing scarcity of coke, melting of cast iron and silicates on natural gas is becoming widely accepted.
Known in the art is a gas cupola comprising a shaft with built-in gas burners and further comprising water-cooled partitions dividing the shaft into two parts, viz. an upper melting chamber and a lower superheating chamber. The water-cooled partitions are provided with a packing of high melting and heat resistant materials (see U.S.S.R. Inventor's Certificate No. 503107, F 27B 1/08, published in 1976).
However this cupola suffers from the disadvantage that molten materials adhere to the water-cooled partitions, which causes drop in the temperature of the melt, reduction of the passages for the movement of the hot gas and the melt between the water-cooled partitions, and increase of heat losses due to heating of the water in the partitions.
Another drawback is the lower superheating chamber which is not filled with a refractory packing and causes heavy heat losses through the walls, thereby decreasing the cupola efficiency and causing lack of the melting temperature.
A still further drawback is that the cupola construction under consideration hampers removal of refractory packing and unmolten materials from the shaft after the melting process and complicates repair of the lining and preparation of the cupola for melting.
Also known in the art is a cupola which is designed for melting cast iron on a refractory packing in the shaft and comprises horizontal-duct burners in the cupola bottom part (see the book by Girshovich N. G. "Iron Casting" published by Metallurgizdat in 1949, pages 633-635, 642-644,654-656).
This cupola suffers from the disadvantage that during operation thereof the burner ducts become blocked with slag molten refractories, the melting process being thereby disturbed. The refractory packing in this cupola is heated unevenly and the gaseous products of combustion poorly penetrate into the refractory packing, owing to which the temperature of the molten material decreases and the quality of castings is adversely affected.
Also known in the art is a gas cupola, which is the prototype of this invention comprising a shaft with burners radially equispaced around the periphery of the cupola bottom part (see the book by I. M. Rafalovich "Natural Gas as Fuel for Metallurgical Furnaces", published by Gosudarstvennoye Nauchno-Tekhnicheskoye Isdatelstvo po Chornoi i Tsvetnoy Metallurgii in 1961, Moscow, pages 150-151).
The cupola in question operates on natural gas and preheated air. The column of the charge materials is supported by a bed of natural corundum and gas is burnt in a corundum packing. However, durability of corundum is insufficient. During prolonged operation the combustion process becomes upset and gas is not uniformly distributed in the refractory bed, whereby the melting process is disturbed and frequently discontinued.